It has long been known that typical city water supplies have a variety of contaminants which contribute to an unpleasant taste of a beverage made from that city water. Among these contaminants are lead, hydrocarbons, calcium, iron, sulfides, and especially chlorine used in purifying the city water. While all of these contaminants contribute to the unpleasant taste of beverages prepared from such city water, chlorine is probably the most usual and troublesome contaminant, since it is normally present in all city water, due to the purification process, and since it can be detected in beverages in very small amounts. While the unpleasant taste of the beverage prepared from such city water is detectable in almost every beverage so prepared, including reconstituted orange juice, soft drinks, iced drinking water, and the like, it is particularly troublesome in connection with beverages which are heated during preparation, e.g. tea and coffee.
The art has long sought effective means of removing such contaminants, especially chlorine, from such city water, and a number of approaches in the art have been taken. For example, one approach is that of a porous plastic film filter with pores sufficiently small to filter contaminants, such as chlorine, from the water, but such filters have a very low gravity flow rate, and to use such filters requires considerable time for filtration of the water in beverage preparation.
Another approach is that of providing a matrix of fibers and activated charcoal where the activated charcoal will remove contaminants, especially chlorine, but to make such filters satisfactory, the fibers must be made of materials which will not support bacterial growth, since, otherwise, continued use of such filters would cause a health problem. To substantially avoid bacterial growth, such filters, with activated carbon therein, are made with hydrophobic synthetic polymer fibers, which are generally non-porous, and hence will not support bacterial growth resulting from absorbed nutrients from the water. However, filters made from such hydrophobic fibers have a very low gravity flow rate, and to be useful in a practical sense, filters of that nature must be operated under substantial pressure, e.g. city water pressure. Thus, filters of that nature have been limited, generally, to "in-line" filters, i.e. filters disposed in the city water pressure lines of a house, manufacturing facility, or the like or at the taps thereof. These filters, therefore, operate generally with city water pressure, e.g. about 40 psi or more. While this arrangement is satisfactory for in-line filters, such an arrangement is not satisfactory for gravity flow filters. In addition, filters of this nature must be contained in a canister and protected by media around the filter for preventing particles of activated carbon from passing through the filter, during use, and into the consumable water. This further decreases the pressure drop across those filters and, consequently, requires the higher city water pressures for effective use thereof.
Efforts have been made in the art to improve flow rates with less pressure for effective use thereof, and U.S. Pat. Nos. 4,395,332; 4,505,823; and 4,569,756 are representative thereof. These patents describe filters for removing contaminants from water, where the filters contain cellulose fibers and an additional strengthening fiber, such as a polyester fiber, as well as a contaminant adsorbent, which, among others, can be activated carbon or charcoal. In addition, these filters contain micro-bits of polymers, which polymers can be, for example, polystyrene polymers, polyolefin polymers and the like. These micro-bits retain porosity in the filters and, therefore, provide greater flow rate with less pressure drop through the filters. Thus, the filters are said to be useful for filtering tap water for drinking and cooking use in a gravity flow filter device and, particularly, a conical filter for filtering tap water from a tap with such conical filter device is disclosed. However, the filters of these patents, while said to be useful in filtering tap water by gravity flow filtration for drinking and cooking purposes, are composed, in a specific example, of cellulose fibers, polyester fibers, activated charcoal, a binder for binding the fibers together to improve the strength thereof, and the micro-bits, which combination still has a very low gravity flow filtration rate. While that low filtration rate is suitable for some purposes, it is not suitable for a variety of other purposes.
In this latter regard, as noted above, beverages which are heated in preparing the beverage are particularly susceptible to the taste of tap water contaminants, especially chlorine, and very typical of such beverages are coffee and tea. Both coffee and tea may be brewed in a conventional coffee making machine, where cold water is heated by an electrical heating element and, after being heated, is fed through a basket containing the coffee or tea by which the brewed coffee or brewed tea is made and discharged from that basket by gravity into a pot. As the art has well appreciated, in order to make a filter suitable for such machines, the filter must have a flow rate consistent with the brewing rate of the machine. Otherwise, the time for brewing, for example, a pot of coffee, would be greatly increased, and the heating element of the machine could be starved for water and burn out or the hot water supplied to the basket containing the tea or coffee could be seriously reduced, and ineffective brewing and long brewing time would result. Thus, gravity filters with such reduced flow rates are not satisfactory for those purposes. Moreover, those patents do not describe any practical means of retaining the activated charcoal in the filter, and any substantial amount of activated charcoal that passes through the filter into the brewed coffee or tea, of course, would be quite unacceptable.
A somewhat similar but yet slightly different approach in the art is described in U.S. Pat. No. 4,160,059, where a filter is proposed that is made of wood pulp and/or synthetic fiber, a heat-fusible fiber, and an adsorptive material, such as activated charcoal. The heat-fusible fiber is heated to fuse the charcoal to the fibers of the filter, which, therefore, presumably locks the activated charcoal particles in place and prevents that activated charcoal from passing through the filter and into a beverage. This fusing of the charcoal particles to the fibers is considered a better approach than that of the prior art where latex binders have been used for binding the charcoal to fibers.
In this latter regard, U.S. Pat. No. 3,158,532 teaches a filter material made of various fibers, including polyester fibers and paper fibers, and a bonding agent or binder for binding particulate material to deposited layers of fibers, and the particulate material, in addition to a number of others, can be activated carbon. Among the binders suggested are polyacrylic resins.
It has also long been recognized that hydrophilic fibers forming a filter material will substantially increase the flow rate of water and similar water-containing fluids through the filter, and commercial milk filters are commonly made of cellulose fibers for this purpose, e.g. cotton, rayon and mixtures thereof. Such filters have also been made with a combination of rayon fibers and synthetic fibers, such as polyester fibers, polyolefin fibers, polyacrylate fibers, and polyamide fibers, in order to provide better physical properties to those filters, and U.S. Pat. No. 3,307,706, is representative thereof.
Various forms of filters using activated carbon have also been described in the art, such as pleated forms and tape-like porous material, and U.S. Pat. Nos. 4,130,487 and 4,645,597 are representative thereof.
From the foregoing, it can be seen that the art has approached filters of the present nature from various directions, but the art has not been successful in providing a filter which will give high flow rates of gravity-filtered water, which will remove substantial amounts of contaminants, especially chlorine, which will ensure that a chlorine absorbent or adsorbent will not be displaced from the filter and into the water for producing the beverage, which will not support bacterial growth with considerable reusage of the filter, and which can be so inexpensively produced as to be practical, especially, for home use, and more especially in conventional coffee making machines. It would, therefore, be of considerable advantage to the art to provide a filter which meets all of the foregoing requirements, and which, in addition, can remove very substantial amounts of contaminants, especially chlorine.